1. Field of the Invention
Embodiments of the invention relate to methods for cleaning optical components within a processing chamber.
2. Description of the Related Art
Semiconductor devices include metal layers that are insulated from each other by dielectric layers. As device features shrink, reducing the distance between the metal layers and between metal lines on each layer, capacitance increases. To address this problem, new insulating materials that have a relatively low dielectric constant are being used in place of silicon dioxide to form the dielectric layer that separates the metal lines. An exemplary material that may be used to form such a low-k dielectric layer is porous carbon doped oxide (CDO). Using this material instead of silicon dioxide to separate metal lines can yield a device having reduced propagation delay, cross-talk noise and power dissipation.
Porous carbon-doped oxides achieve lower dielectric constants through the incorporation of non-polar covalent bonds (e.g., from the addition of carbon) and the introduction of porosity to decrease film density. Introducing porosity or the incorporation of terminal bonds, such as Si—CH3, breaks the continuity of the rigid Si—O—Si lattice of oxides, yielding a lower dielectric constant film that is both mechanically and chemically weaker. Because of the mechanical weakness, porous carbon-doped oxides are susceptible to damages caused by plasma etching and ashing processes that are known to lead to subsequent moisture uptake which detrimentally increase the dielectric constant to unacceptable levels. Therefore, a k-restoration process, such as a silylation process, is typically performed to repair at least some of the damage to the porous carbon-doped oxides.
The silylation process repairs the damage by replacing hydrophilic bonds with hydrophobic bonds. For example, a silylating agent such as methyl or phenyl containing compounds may be introduced into a chamber to react with the Si—OH groups in low-k films to convert the hydrophilic Si—OH groups into hydrophobic groups to reduce moisture uptake, thus decreasing dielectric constant. A UV (ultra violet) curing process may be optionally performed in-situ or in a separate chamber to accelerate the reaction and/or seal pores in the low-k films.
During the silylation process, various exposed surfaces of the chamber components, such as the quartz based vacuum window, showerhead, and chamber walls etc., presented in the chamber can become coated with repairing chemicals, resulting in degradation of the UV source efficiency or particle contamination of the substrate during subsequent processing. The build-up of these silylation coating or residues on the chamber components requires periodic cleaning, which results in significant tool downtime and a corresponding reduction in throughput.
Therefore, a need exists to clean silylation residues on the chamber components and increase UV efficiency.